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I have Windows 10 installed in UEFI mode. I tried dual booting Ubuntu 14.04 with Windows by using bootable flash drive (I used Rufus for this). But the flash drive doesn't get detected in UEFI mode; it only gets detected in Legacy mode.

I followed both the answers to this question on Super User. I even tried placing the bootx64.efi file inside the boot folder but it was no use. So I thought of installing Ubuntu in legacy mode temporarily. What problems might I face?

Zanna
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aanchal
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    You may have to turn on allow USB boot for it to work. Ubuntu installer is correctly configured to boot in either UEFI or BIOS/CSM mode. If newer computer you may need 16.04 to have newer kernel & drivers. What brand/model system? UEFI only boots from /EFI/Boot/bootx64.efi on external devices. System should work in Legacy mode, but you need a bios_grub partition which it should create. And if drive is gpt, you can convert to UEFI if you also have an ESP - efi system partition. https://help.ubuntu.com/community/UEFI – oldfred Jun 05 '17 at 14:55
  • my laptop is acer F5-573G. I had windows 10 pre-installed in UEFI mode. – aanchal Jun 05 '17 at 15:27
  • There is a possibility you will break windows if you do that. 14.04 is long in the tooth, why not a more recent version of Ubuntu such as 16.04 which is also a LTS. – Panther Jun 05 '17 at 15:37
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    Acer needs you to set a supervisor password, then you get other menu items and can set trust on the usb and hard disk. see https://ubuntuforums.org/showthread.php?t=2362963 I dual boot the other way, Windows 10 legacy, Ubuntu 17.04 UEFI, but have separate disks, and a Lenovo which switches modes automatically. – ubfan1 Jun 05 '17 at 15:54
  • Anyone who attempts dual booting without reading https://en.wikipedia.org/wiki/Power-on_self-test , https://en.wikipedia.org/wiki/BIOS , https://en.wikipedia.org/wiki/Master_boot_record , https://en.wikipedia.org/wiki/GUID_Partition_Table , https://en.wikipedia.org/wiki/UEFI is doomed to confusion, failure and frustration. – waltinator Jun 05 '17 at 16:23
  • ubfan1 thank you. I followed the instructions from the link you shared and it worked. But I've now come accross another problem. I installed ubuntu and on restart I don't see grub menu. I already disabled fast start up and hibernate in windows 10 but I still dont see the grub menu. – aanchal Jun 06 '17 at 02:55
  • There is a worthy question here (in the title) and it has been answered. Voting to leave open. If you need further help actually completing you installation, I suggest you ask a new question with a link to this one, as the subject is drifting. – Zanna Jun 07 '17 at 04:56

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Note the references provided in comments to your question. It should be possible to install Ubuntu directly in EFI mode on your computer, whether by mucking with the Acer-specific security configuration, by preparing the USB flash drive directly (see this page of mine for some tips on doing this), or in some other way.

If that fails, it may be possible to install Ubuntu in BIOS/CSM/legacy mode but to then convert it to boot in EFI/UEFI mode by installing an EFI boot loader for Linux. Most people do this by running Boot Repair from an Ubuntu emergency disk; but if you're not able to get one of these to boot in EFI mode, this may not be an option. In this case, installing my rEFInd boot manager in Windows, along with the EFI filesystem driver for whatever filesystem holds your kernel (ext4fs by default) may do the job.

Mixed-mode (BIOS/EFI) OS installs pose problems with boot loader management. Depending on your firmware, switching the OS to be booted ranges from a bit awkward to impossible. I can't say where on the continuum your system would fall because I'm not familiar with recent Acer computers or their firmware. The usual best-case scenario is that you'd have to hit a special key (usually a function key, Esc, or Enter) as the computer starts to launch the EFI's built-in boot manager. This will then enable you to select whether to boot in BIOS mode (therefore launching GRUB and Ubuntu) or to boot any of the installed EFI boot loaders (most or all of which would boot Windows). The keypress to get to the EFI's boot manager, though, must usually be hit in a narrow window of time, and on many computers, getting it to activate can be a bit hit-or-miss. In some cases, the boot manager shows only BIOS options or only EFI options, depending on firmware settings, so you might need to go into the firmware setup utility to reconfigure the boot mode before you can switch between OSes. In the worst case I've seen, switching boot modes is impossible because it depends on things like the partition table used on the disk.

In some cases, my rEFInd boot manager can help. If you edit its refind.conf file to uncomment the scanfor line and ensure that hdbios is among the options, rEFInd supports booting BIOS-mode boot loaders as well as EFI-mode boot loaders. In your specific case, though, this is unlikely to be helpful because if you can get rEFInd to launch by default, it should be able to boot a Linux kernel in EFI mode, so there's likely to be no benefit to launching GRUB (and Linux from there) in BIOS mode from rEFInd. rEFInd might be more helpful if you had Ubuntu installed in EFI mode alongside a BIOS-mode Windows installation (likely on a second disk).

Rod Smith
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  • I was able to install ubuntu by setting the supervisor password and going to the trust settings. But I again have another problem. The installation was complete but on restart I didn't see the grub menu. I already disabled the hibernate and fast start up opptions in window 10. – aanchal Jun 06 '17 at 02:59
  • See this question and its answers for suggestions on dealing with the no-GRUB issue. – Rod Smith Jun 06 '17 at 12:56